1. Field of the Invention
The present invention relates to a window display control device which is used for displaying window picture images on a CRT image plane or the like, and particularly to a window display control device which enables high speed data display in a virtual window region on renewal of the image plane.
2. Description of the Prior Art
FIG. 1 is a block diagram to schematically show construction of a conventional window display control device.
As shown in the same diagram, a window display control device 1 comprises a buffer memory 2, data process means 3, an virtual image plane memory 4, window control means 5 and a view port memory 6.
In the buffer memory 2, an output data from a data process device is contained. The data process means 3 converts the output data contained in the buffer memory 2 into display data.
In the virtual image plane memory 4, the display data converted by the data process means 3 are contained. The window control means 5 retrieves only display data in a virtual window region 4a separately designated in the virtual image plane memory 4 in accordance with a predetermined display start command.
In the view port memory 6, the display data retrieved by the window control means 5 are contained. The data contained in the view port memory 6 are displayed in a CRT image plane 7.
As described above, only the display data contained in the virtual window region 4a of those contained in the virtual image plane memory 4 are displayed in the CRT image plane 7, and when the virtual window region 4a is suitably moved, a window image displayed on the CRT image plane also moves.
However, in such a conventional window display control device, when the display data in the virtual image plane memory 4 are renewed, the window control means 5 is arranged so as not to retrieve data in the virtual window region 4a until all of the renewal of the renewal data supplied from the data process means 3 is completed. Accordingly, as shown in FIG. 2, when an amount of output data 8 localized in the virtual window region 4a is small as compared with a size of the entire body of an output data 9, since the output data 8 are actually displayed on a screen after a renewal process of all the data is completed, the display speed of the data 8 becomes very low even though the amount thereof is small.
This problem becomes remarkable as the amount of the output data localized in the virtual window region 4a is small as compared with the size of the entire body of the output data 9.